1. Field of the Invention
The present invention is concerned with an improved electrical vacuum switch which includes a spring-biased, shock-absorbing member for controlling the closing sequence of the switch in a manner to prevent significant, deleterious deformation of the soft metal contact shafts of the switch. More particularly, it is concerned with a switch of the type described in U.S. Pat. No. 3,562,454 wherein a low mass weld break lever is employed, in conjunction with a helical biasing spring, in order to provide a desirable shock-absorbing function while at the same time allowing the switch to be closed and opened in the usual fashion.
2. Summary of the Invention
Vacuum switches are well known and normally include a vacuum bottle which encloses a pair of separable contacts respectively supported by a stationary and shiftable shaft. In order to retain their electrical operating characteristics, such switches are formed of specialized materials and fabricated in ways to avoid formation or release of ionizable gases such as oxygen within the vacuum bottle. For example, it is common to use oxygen-free copper for the contact-supporting shafts, and to subject the bottle, shafts and contacts to a high temperature (1000.degree. C.) degassing and brazing procedure during manufacture. While this technique greatly lowers the possibility of oxidation during manufacture and use of the switch, the high temperature process adversely affects the copper contact-supporting shafts and renders the same soft and deformable. As a result, opening and closing operations with the switches tends to deform and in effect shorten the contact shafts (by as much as 1/4 inch); and this alteration drastically changes the operating characteristics of the switches.
U.S. Pat. No. 3,562,454 describes a vacuum-type electrical switch having a pair of separable contacts and an over toggle spring-operated opening and closing mechanism. In addition, the subject patent describes a weld break lever associated with the operating mechanism which assures opening of the switch contacts even in the event that the latter become welded together during use. In order to facilitate a description of the present invention, U.S. Pat. No. 3,562,454 is hereby expressly incorporated by reference into the instant specification.
The over toggle operating mechanism described in the above-referenced patent is extremely effective for quickly and positively opening and closing the associated switch contacts. As can be appreciated, it is desirable in switch units of this type to rapidly close and open the contacts so as to substantially eliminate arcing over or decomposition of the contacts themselves. By the same token however, it is known that switch contacts can be effectively welded together during use thereof, and unless some positive weld break feature is provided, the extremely dangerous situation can result wherein a lineman can trip open the switch actuating mechanism while the contacts themselves nevertheless remain in conductive engagement. In order to overcome this problem, U.S. Pat. No. 3,562,454 describes the use of a J-shaped auxiliary weld break lever which is pivotally mounted adjacent the over toggle mechanism and located for contact with the operating mechanism during the closing sequence. If the contacts are welded together, continued rotation of the operating arm of the switch acts, through the J-shaped lever, to positively break the weld and thus open the contacts.
Switches of the type described in U.S. Pat. No. 3,562,454 are normally provided with the soft copper contact shafts described above, and the problems of shaft deformation are present in these units.
In the past, the problem of shaft deformation has been partially alleviated by multiple openings and closings of newly manufactured switches prior to use thereof in the field. For example, it has been the practice to go through the total of 225 separate opening and closing operations in order to work harden the originally deformable contact shafts, and thereafter readjust the switch operating mechanism for proper opening and closing prior to shipping thereof.
Although this procedure largely solves the problem of shaft deformation, it will be appreciated that it is costly from a manufacturing standpoint. Moreover, in view of the fact that 225 opening and closing sequences is far in excess of the normal number of such sequences experienced by a switch during the useful lift thereof, it can be seen that the procedure represents a significant wear and tear on the switches, and that this occurs before the same ever go into actual use.